Cigarette paper and method for preparation

ABSTRACT

Cigarette paper having improved taste and aroma during pyrolysis wherein the paper is loaded with an agent comprising up to 45 percent by weight calcium oxalate preferably formed in situ internally in the paper fibers and/or conversion of the cellulosic fibers by selective oxidation to convert preferably 40 to 60 percent of the methylol groups on the C6 position to carboxylic acid groups and further treatments.

tates Patent [151 3,64%25 111m Brisltin et a1. Feb. b, 1972 [54]filGARETTE PAPER AND METHOD [561 References Cited FOR PREPARATION UNITEDSTATES PATENTS [72] Inventors: Theodore Briskin; Geoffrey R. Ward, bothof Beverly Hills Cam 3,447,539 6/1969 Bnskm et a1 ..l31/2 3,478,75111/1969 Briskin et 31.... [73] Assignee: Sutton Research Corporation,Los An- 3,473,752 1/1969 Briskin et 81....

geles, Calif. 3,491,766 l/1970 Briskin et al Ill 5 X Filed; 17, 1968FOREIGN PATENTS OR APPLICATIONS [21] Appl. No.: 784,472 702,918 2/ 1965Canada l 3 H2 Related U'S Apphmuon Data Primary Examiner-Howard R. Caine[63] Contimiation-in-part of Ser. No. 745,372, July 17,AmmeyMcDougall,fiershficotwledd 1968, abandoned, which is acontinuation-in-part of Ser. No. 595,622, Nov. 21, 1966, Pat. No.3,447,539, ABSTRACT and a continuationinpm of 674,994 1967 Cigarettepaper having improved taste and aroma during abandoned pyrolysis whereinthe paper is loaded with an agent comprising up to 45 percent by weightcalcium oxalate preferably formed [52] US. Cl ..13l/2, 131/15, 162/139,in Sim internally in the paper fibers and/or conversion of the 162/157162/179 260/212 cellulosic fibers by selective oxidation to convertpreferably [51 Int. Cl ..A24b 15/00, A24f3/00, D21f 1 1/00 40 to 0percent of h methylol groups on the C8 i i to [58] Field of Search 162/139, 157 C, 179; 131/2, carboxylic acid groups and f th u-eatmemsl31/l5;260/2l2 24 Claims, N0 Drawings CKGARETTE PAPER AND METHOD FORPREPARATION This is a continuation-in-part of our copending application,Ser. No. 745,372, filed July 17. 1968 and titled Cigarette Paper andMethod for Preparation, now abandoned which in turn is acontinuation-in-part of the copending application, Ser. No. 595,622,filed Nov. 2i, 1966, and titled Smoking Products," now Pat. No.3,447,539 and Ser. No. 674,994, filed Oct. 12, i967, and titled SmokingProducts and Process for Making Such Products now abandoned.

in the aforementioned copending applications, description is made of thepreparation of a smoking product suitable for cigarettes, cigars, orpipes, in which relatively pure cellulosic material is subjected toselective oxidation with liquid nitrogen dioxide to convert more than 90percent of the free hydroxyl groups on the cellulosic molecule tocarboxyl groups to yield a product which can be referred to as anoxycellulose. The oxidation reaction product is further processed byremoval of the liquid nitrogen dioxide by vaporization and washing ofthe oxidized product with water and/or alcohol for removal ofsolubilized foreign materials and/or treatment with solvents, such asacetone for removal of oils, waxes, lattices and the like whichcontribute undesirably to the taste and odor when the product is used asa smoking product.

As further described in the aforementioned copending applications, theoxidized and cleansed cellulosic derivative is further processed by areduction reaction with a hydride or borohydride of an alkali oralkaline earth metal, such as sodium, or lithium borohydride, forreducing groupings which otherwise have a tendency to evoke unpleasantodors or taste as the product is pyrolized. The product before or afterbeing processed by the described reduction reaction can be subjected tooxidation with peroxide solutions as a means for eliminating furthercomponents which contribute undesirable aroma or taste to the productduring pyrolysis.

The resulting oxidized and reduced cellulosic material is thenformulated with mineralizing agents to the form of oxalates lactates,pivalates or tannates of such metals as calcium, magnesium, lithium,potassium, barium or strontium, preferably introduced internally,preferably within the cellulosic derivative for purposes of providingdesirable ashing characteristics, although beneficial ashingcharacteristics of limited utility can be achieved by externalapplication of such mineralizing agents to coat the fibers or foradmixture with the fibers. As described, the desired internalapplication of the mineralizing agents can be achieved by first wettingthe fibers with a solution of the desired metal ion for absorption intothe cellulosic derivative, followed by exposure to a solution of thedesired anion whereby the corresponding metal salt forms in situ withthe cellulosic material.

Maintenance of glow and burning rate, characteristic of tobacco, isachieved by formulation to include a potassium salt, such as potassiumoxalate, or by the addition of rubidium or cesium compounds in amountswithin the range of l percent to percent by weight but preferably lessthan 1 percent by weight, as described in the copending application Ser.No. 623,528, filed Mar. 16, 1967, and titled Smoking Products andProcess for Their Manufacture now abandoned. Smoke generators can beadded to increase the visual effect of the smoking product when burned.

The resulting product is suitable for use as a smoking product alone orin admixture with tobacco to produce a smoking product having bettertaste and less undesirable ingredients in the smoke.

The concept of this invention resides in the improvement of the paper orsheet material in which the tobacco or the smoking product is rolled inthe fabrication of cigarettes, cigars, or the like smoking products.

To the present, use is made of cigarette paper formed of purifiedcellulose pulp loaded with about percent to 30 percent by weight calciumcarbonate with small amounts of other possible modifiers. Pyrolysis ofthis paper gives a most un' desirable irritant odor which, thoughdiluted with the smoke from the tobacco, undesirably affects the odorand taste of the smoking product. Many of the attributes obtained fromthe improved smoking product prepared of cellulosic materials, asdescribed in the aforementioned copending applications, are upset inpart by the use of conventional cigarette paper or wrappers.

Thus, it is an object of this invention to product and to provide amethod for producing a paper or wrapper of cellulosic material which ischaracterized by having improved odor, taste, and aroma during pyrolysiswhereby cigars and cigarettes currently produced with tobacco canmaterially be improved, at least from the standpoint of taste and aroma,and wherein the balance of good taste and aroma of cigars and cigarettesproduced in cellulosic materials in the manner described in theaforementioned applications are not materially upset by the wrapper orpaper in which the smoking material is incorporated.

It is a further object of this invention to provide a number of methodsand means which individually operate to provide a more desirable paperor wrapper from the standpoint of taste and aroma and which, in variouscombinations, offer still greater improvement when utilized as a part ofa smoking product.

The invention will be described with reference to paper formed ofpurified cellulose or woodpulp, such as alpha-cellulose, but it will beunderstood that the term cellulose is in tended to include othercellulosic fibers and materials of the type used in the making of paperand the like wrapping material.

First, with reference to cigarette paper as it is now prepared frompurified cellulose loaded with 20 percent to 30 percent by weightcalcium carbonate, considerable improvement is derived by the treatmentof cigarette paper with a dilute solution of oxalic acid containing from1 percent to l0 percent by weight oxalic acid in a dissolved state in anaqueous medium at a temperature within the range of room temperature toC.

The oxalic acid solution operates to convert calcium carbonate toinsoluble calcium oxalate. The latter is sufficiently stable thermallyto remain while the cellulosic material is pyrolyzed during the smokingof the cigarette so that the effect of calcium on the odor is minimizedand a cleaner tasting cigarette is obtained. During the final stages ofthe pyrolysis, the calcium oxalate breaks down to calcium oxide andcalcium carbonate which remain as ash and carbon dioxide and/or carbonmonoxide gas which goes off with the smoke and is substantially odorlessand tasteless.

Treatment with oxalic acid does not interfere with the desirablecharacteristics of the paper for its intended use as a wrapper.Treatment with oxalic acid can be effected by passing the preformedpaper web through an aqueous solution of oxalic acid at a rate toprovide a residence time sufficient to achieve the desiredtransformation (about 2 to l0 minutes), after which the web is washedwith water to remove excess oxalic acid or other solubles present in theprocessed paper.

Improvement in the smoking characteristics of the paper wrapper incigarettes is achieved, in accordance with the practice of thisinvention when thecalcium oxalate and/or magnesium oxalate orcorresponding mineralizing agent, as described herein, is present in thepaper in an amount greater than 5 percent by weight but it isundesirable to make use of an amount greater than 45 percent by weightand it is preferred to make use of a cigarette paper containing 10-40percent by weight of such mineralizing agent.

It will be understood. Of course, that the desired construction can beobtained by the substitution of calcium oxalate and/or magnesium oxalatefor calcium carbonate in the finish or slurry of cellulosic pulp used inthe original formation of the paper web.

instead of oxalic acid, use can be made of pivalic acid or tannic acidto form the corresponding pivalate or tannate. lnstead of calcium, usecan be made of magnesium, barium, or strontium to provide thecorresponding magnesium, barium, or strontium oxalate, pivalate, ortannate in the cigarette paper and it is preferred to make use of thecombination of a major proportion of calcium and a minor proportion ofmagnesium as the cation of which the filler is formed.

By way of modification of this initial concept, it has been found thatstill further improvement in the smoking characteristics of the papercan be obtained when a small amount of free pivalic, tannic andpreferably oxalic acid is reintroduced or otherwise provided in thecigarette paper. The function of the free acid returned to the treaterpaper is to ensure that small amounts of ions of heavy metals, such ascalcium, barium, strontium, magnesium, copper, cobalt, iron, andaluminum remaining in the paper or subsequently released are taken up toform the corresponding insoluble heat-stable oxalate, tannate orpivalate, as the case may be. For this purpose, it is undesirable toprovide for more than 0.5 percent by weight acid since excessive amountsof oxalic or the like acids are objectionable from the standpoint of thetaste and aroma which additional amounts thereof contribute to theproduct when it is smoked. When employed, it is preferred to introducethe oxalic or like acid in an amount within the range of 0.l percent to0.25 percent by weight. Reintroduction can be made by dissolving thecalculated amount of acid in an aqueous medium to provide a solutioncontaining 0.1 percent to l percent by weight of the acid and thenspraying the solution onto the web or by passing the web through asolution followed by drying, or by mixing the solution with the pulpfiber slurry during the paper making.

The foregoing concepts will now be illustrated by way of the followingexamples.

EXAMPLE 1 Cigarette paper, already formed, is passed through a bathheated to 30 C. and formed of an aqueous solution containing 5 percentby weight oxalic acid. Passage is made at a rate to provide a residencetime ofabout 5 minutes.

Upon emergence from the bath, the treated web is subjected to two orthree washings with water to remove excess oxalic acid or other watersolubles. A controller excess of oxalic acid is then applied by sprayingthe treated and washed and semidried paper with an aqueous solutioncontaining 0.2 percent by weight oxalic acid in an amount to provideabout 0.1 percent by weight free acid in the paper. The paper is finallydried to about 40 percent relative humidity.

Tannic acid can be substituted, in whole or in part, for the oxalic acidin equivalent amounts in Example 1.

EXAMPLE 2 Purified cellulose pulp is slurried with a mixture of calciumoxalate and magnesium oxalate in the ratio of about four parts by weightcalcium oxalate to one part by weight magnesium oxalate with the totaloxalate present in an amount to make up about percent to 40 percent byweight of the solid of the fibrous slurry.

The slurry is used as a furnish in a conventional papermaking machine toproduce a cigarette paper fabricated of cellulosic fibers containing 20percent to 40 percent by weight of calcium and magnesium oxalate.

For the embodiment wherein calcium and/or magnesium oxalate is embodiedin the paper, or in the fibrous materials with which the paper isformed, it is preferred to take advantage of the lapse of time betweenthe admixture of the calcium cation and the oxalic acid anion to theprecipitation of an insoluble calcium oxalate to achieve fullerpenetration or impregnation of the cellulosic system. It appears thatcalcium oxalate remains in the dissolved state in a highly hydrated formfor a length of time sufficient to enhance penetration of impregnationof the cellulosic system. It appears that calcium oxalate remains in thedissolved state in a highly hydrated form for a length of timesufficient to enhance penetration or impregnation of the cellulosicsystem, before precipitation of calcium oxalate in response toseparation to water of hydration. This same effect is experienced withthe combination of magnesium and oxalic acid, only at a slower rate.

ln practicing this phase of the invention for introduction of calciumand/or magnesium oxalate, separate aqueous solutions are preparedcontaining the calcium cation in one solution in an amount within therange of 1-15 percent by weight and preferably 3-7 percent by weight,while the other aqueous solution contains the oxalic acid anion inequivalent amounts. The two solutions are admixed immediately prior toapplication with the cellulosic material or the separate solutions areapplied substantially simultaneously to the cellulosic material or paperweb, followed by drying.

Reapplication can be made a number of times until the desiredconcentration of ashing ingredients is inserted within the cellulosicsystem.

As in the preceding case, the calcium and magnesium can be substitutedwith barium or strontium and the oxalic acid can be substituted withtannie, pivalic, glyeolic, diglycolic, or lactic acid.

The following example will illustrate the practice of this phase of theinvention.

EXAMPLE 3 Purified cellulose pulp is slurried with 25 times its weightof a freshly prepared mixture of equal parts of5 percent solution ofcalcium acetate and a 5 percent solution of oxalic acid. The slurry iscast on a screen in the usual manner for the formation of cigarettepaper. The calcium acetate and oxalic acid do not immediately react toform an insoluble calcium oxalate, especially when the slurry ismaintained at ambient temperature or below. As a result, the componentsare capable ofsoaking into the cellulose fibers before the calciumoxalate is precipitated to provide internal loading in situ in thefibers with the mineralizing agent. This pulp is then dried, the processrepeated a number of times until the desired ash level is achieved. Thecalcium oxalate can be added as an insoluble compound for suspensionwith the pulp to provide a concentration within the range of 10 to 45percent but best results are secured, especially from the standpoint ofthe characteristics of the ash, when the oxalate and the likemineralizing agent is formed internally within the pulp fibers. Theformed paper is washed with water to remove water solubles includingacetic acid formed upon replacement by oxalic acid and any excess oxalicacid or calcium acetate, as the case may be. Free oxalic acid can bereintroduced as in Example I or the free acid can be omitted.

When, instead of conventional cigarette paper, use is made of paperprepared as in Examples l to 3, a cigarette is produced having betteraroma and taste when burned. When used in the preparation of a cigaretteor cigar with a smoking product prepared of cellulosic material, asdescribed in the aforementioned copending applications, the taste andaroma of the smoking product are upset less by the paper wrapperprepared in accordance with Examples 1 to 3 as compared withconventional cigarette paper,

This is an improvement which is important to the current field ofsmoking products since it provides for better taste and odor to currenttobacco products as well as to synthesized smoking products of any type.

A second concept of this invention resides in the practice wherein theprepared cigarette paper, and preferably the purified cellulose pulp ofwhich the cigarette paper is formed, is treated to effect selectiveoxidation of the methylol groups on the C position of the cellulosemolecule with permissible oxidation at the C and/or C position toproduce a preferably partially oxidized cellulose hereinafter referredto as oxycellulose in which the oxidation reaction product may becomprised of polyuronic acids and their derivatives.

In the practice of this modification of the invention, the amount ofoxidation of the cellulosic material should be limited to within therange of 15 to percent calculated on the conversion of the methylolgroup on the C position of the cellulose molecule. It is preferred toprovide for an oxycellulose in which the level of oxidation has beenlimited to within the range of 40 to 60 percent. Below the level ofpercent oxidation the improvement of odor and taste during pyrolysis ofthe paper is not significant. Above an oxidation level of 60 percent,the oxycellulose tends to lose some of its fibrous characteristics suchthat the oxycellulose pulp becomes less capable of being interfelted andtherefore less suitable for use in the preparation of a paper ofsufficient strength and integrity for use as a cigarette wrapper.Previously formed paper oxidized to a level beyond 60 percent similarlybecomes less suitable for use. When the oxycellulose is characterized bymore than 60 percent oxidation, the oxycellulose can be blended withconventional pulp for use in the fabrication of cigarette paper but itis important to have a blend in which at least 15 percent of the totalmethylol groups have been oxidized in order to achieve significantimprovements. Within the preferred range of 40 to 60 percent oxidation,the oxycellulose retains sufficient of its fibrous characteristics toenable use of the already formed cigarette paper or to enable use of theoxycellulose pulp in the preparation of cigarette paper by conventionalpaper-forming machines.

ln effecting the desired level of selective oxidation, it is preferredto make use of nitrogen dioxide as the oxidizing medium. Since thepreferred level of oxidation is substantially less than that forcomplete oxidation, it is possible to make use of gaseous nitrogendioxideas the oxidizing medium. However, from the standpoints ofoxidation rate, uniformity of oxidation and process control, it ispreferred to make use of liquid nitrogen dioxide, especially in thetreatment of previously formed cigarette paper. The oxidation reactionwill hereinafter be described with reference to the use of liquidnitrogen dioxide as the oxidizing medium but it will be understood thatcorresponding results can be achieved by the use of gaseous nitrogendioxide.

Liquid nitrogen dioxide offers a number of advantages over gaseousnitrogen dioxide or other oxidizing agents in that liquid nitrogendioxide gives the desired selectivity in oxidation of methylol on the Cposition of the cellulose molecule. Liquid nitrogen dioxide operatesimmediately and completely to wet the cellulosic fibers so that all ofthe cellulosic material is subject to immediate and uniform oxidation.Further, liquid nitrogen dioxide is available to quench hot spotswhereby heat generated by the exothermic oxidation reaction isimmediately dissipated thereby to avoid the creation of hot spots whichmight otherwise lead to combustion.

Still further, it is possible to effect modifications in the use ofliquid nitrogen dioxide whereby the reaction rate can be increased tolevels suitable for continuous processing. When use is made of liquidnitrogen dioxide as the oxidizing medium, treatment can be made with anamount of liquid nitrogen dioxide, one to one thousand times thecellulosic material and preferably 25 to 50 times the cellulosicmaterial on a weight basis. The oxidation reaction should be carried outwith the materials at a temperature within the range of 15 to 65 C. andunder autogenous pressure. Reaction at temperatures below 15 C. is tooslow for commercial practice and reaction at temperatures in excess of65 often leads to undesirable side reactions and the production of anunstable product under the conditions of use.

Within the defined range of reaction conditions, oxidation is continueduntil the desired level of oxidation is achieved, as measured bytitration to determine the amount of conversion of methylol to carboxylgroups. At C., the desired level will be obtained in about 4 days for 90to 95 percent oxidation and in about 1 day for 40 to 60 percentoxidation. At higher reaction temperatures of 40 to 45 C., the reactiontime will be reduced to the matter of an hour or less for 40 to 60percent oxidation and about 1 day for 90 to 95 percent oxidation.

It is possible to modify the liquid nitrogen dioxide system to includewater in the reaction medium provided that the temperature of thereaction is maintained at a level sufficiently high to counteractexcessive ionization in the medium, as measured by its electricalconductivity. It is believed that when the medium is conductive, thewater in the nitrogen dioxide is in the fonn of nitric (and nitrous)acid which is capable of attacking and/or degrading the fibrouscellulosic material. Thus it is desirable to avoid formation of nitricor nitrous acids in the oxidizing medium. We have found that theelectrical conductivity of a liquid nitrogen dioxide solution containingas little as 1 percent by weight water is very high at 0 but that thesolution becomes substantially nonconductive at 20 C. The conversationrange from conductivity to nonconductivity rises in temperature withincreased concentration of water in the reaction medium. However, whenoxidizing to a level of percent, it is undesirable to make use of morethan 8 percent by weight water in the liquid nitrogen dioxide system andwhen oxidizing to a level within the preferred range of 40 to 60percent, an upper limit of about 10 percent by weight water in theoxidizing medium is established before the oxycellulose tends to betaken into solution.

On the other hand, the presence of water in the liquid oxidizing medium,which is rendered relatively nonconductive bygoing to elevatedtemperature, is effective to accelerate the rate of oxidation so thatthe combination of water and elevated temperature permits the desiredlevel of oxidation to be achieved in a fraction of the time required forthe liquid nitrogen dioxide alone. Thus means are provided to reduce theresidence time of the fibrous cellulosic materials to achieve thedesired level of oxidation.

In the preferred practice of this concept, it is desirable to make useof an oxidizing medium of liquid nitrogen dioxide containing 0.5 to 5percent by weight water and preferably L5 to 3.5 percent by weightwater. At a temperature of 40 to 45 C., an oxidation level of 40 to 60percent can be reached in a matter of minutes to hours thereby to permitoxidation as a continuous operation by passage of the paper continuouslythrough the oxidizing medium under autogenous pressure By way of stillfurther modification, dependent upon the use of liquid oxidizing medium,such as liquid nitrogen dioxide, with or without water, the rate anduniformity of oxidation can still further be improved by means ofintroduction into the reaction medium of gaseous oxygen or a molecularoxygencontaining gas, such as air or oxygen-enriched air, but in whichany gas in which the oxygen is included is an inert gas. The oxygen notonly serves as a means to agitate or stir the ingredients, but, moreimportantly, it provides an oxidizing function of its own in thepresence of nitrogen dioxide thereby to contribute to the oxidation andthe rate of oxidation of the cellulosic fibers. It operates further inthe system to oxidize formed nitric oxide to nitrogen dioxide thereby tomaintain the level of oxidizing medium in the system. When used, theamount of oxygen used should range from equimolecular proportions withthe cellulosic segments making up the cellulosic material (such asglucose or hexose) to about twenty times the theoretical amount, asdescribed in our copending application Ser. No. 745,134, filed July 16,1968, titled Cellulosic Smoking Product and Method in the Preparation ofSame," now US. Pat. No. 3,478,752.

The presence of calcium oxalate or other corresponding mineralizingagent heretofore described does not interfere with the reaction ofoxidation of the cellulosic fibers, whether in the form of paper orpulp. As a result, the described oxidation reaction can be carried outwith pulp or paper embodying calcium oxalate or other mineralizing agentor it can be carried out with paper or pulp in the absence of suchmineralizing agent.

Having generally described the basic concepts of the modification forproviding a pulp for the manufacture of paper or a paper ofoxycellulose, examples will now be given by way of illustration, but notby way of limitation, of the practice of this concept of the invention.

EXAMPLE 4 Cigarette paper, previously formed of purified woodpulp, isimmersed in times its weight of liquid nitrogen dioxide and maintainedat a temperature of 20 C. until 50 percent of the C methylol groups havebeen oxidized to carboxyl groups (about 2 days). During this period, airis bubbled through the reaction vessel at a rate of to 50 parts byweight per part by weight of cellulosic material, spread over thereaction time. The oxidized cellulosic material still retains itsfibrous characteristics such that the paper still has strength andintegrity and can be passed through two to three water washes whereindeionized water is flushed through the oxidized paper. The paper isdried to about 40 to 50 percent relative humidity and calendered forsubsequent use in the conventional manner as cigarette paper.

EXAMPLE 5 Purified woodpulp is introduced into a pressure vessel with 50times its weight of liquid nitrogen dioxide containing 1.5 percent byweight water. The mixture is maintained under a constant state ofagitation by recirculating a small stream of the liquid oxidizing mediumfrom the bottom to the top of the reaction vessel. The reactants aremaintained at a temperature of about 35 to 40 C. and the autogenouspressure and reaction is continued until 40 to 60 percent of themethylol groups on the C position have been oxidized (about 2 hours).When reaction is completed, the liquid oxidizing medium is drawn off andthe oxycellulose is washed several times with water.

The oxycellulose can be suspended in aqueous medium to form a slurrywhich can be employed in the conventional manner to form cigarette papersince the oxycellulose still retains sufficient of its fibrouscharacteristics for interfelting by the paper forming machine to producea cigarette paper which can be processed and used in the conventionalmanner.

EXAMPLE 6 The process of Example 5 is repeated with the cellulosic pulpof Example 3 containing to 45 percent by weight ofinternally formedcalcium oxalate.

EXAMPLE 7 Purified cellulose pulp is introduced into a pressure vesselwith 30 times its weight ofliquid nitrogen dioxide containing 2 percentby weight water. The reaction is carried out under 30 psi. with thematerials maintained at a temperature of 35 C. until more than 90percent of the methylol groups on C have been oxidized (about 4 to 5hours). When oxidation has been completed, the liquid oxidizing mediumis drawn from the vessel and the oxycellulose is washed first withanhydrous nitrogen dioxide to remove moist nitrogen dioxide and solubleimpurities such as gums, waxes, lignins, natural resins, and the like.After evaporation of the anhydrous nitrogen dioxide, the material isthen washed with water to wash out nitric acid and water-solublecomponents. Unlike Examples 4 to 6 wherein the oxycellulose retainsfibrous characteristics sufficient to enable interfelting to formcigarette paper, the cellulosic material oxidized to better than 90percent no longer retains sufficient of its fibrous characteristics toenable fabrication into a paper of sufficient strength or integrity foruse as cigarette paper.

The oxycellulose of Example 7 is admixed in the ratio ofone part byweight oxycellulose to 0.5 to l part by weight of unmodified, purifiedpapermaking wood pulp and the materials are slurried in aqueous mediumhaving a pH below 7 and preferably within the range of4 to 6 to preventsolution of the oxycellulose. Powdered calcium oxalate is included inthe slurry in amount sufficient to give an ash of 23 percent in thefinished paper. The slurry is processed in the conventional manner forpaper making by casting on a Fourdrinier screen for interfelting of theoxycellulose and pulp fibers in uniform distribution for paperformation. The paper after being dried and calendered can be used ascigarette paper in the preparation ofcigarettes, cigars and the like.

The papers of Examples l to 7 can be used in the conventional manner ascigarette paper or cigarette wrappers with smoking products of the typeproduced in accordance with the aforementioned copending application orwith tobacco or with mixtures thereof, or with other materials capableof use as a filler for smoking in cigarettes and cigars.

A remarkable difference will be observed from the standpoint of amarkedly improved and milder odor, aroma and taste when cigarette paperof Examples 4 to 7 is employed instead of conventional cigarette paperin cigarettes, cigars, and the like. This vast difference can bedetected when conventional cigarette paper is pyrolyzed alone in aclosed vessel to seal in the odor for comparison with the pyrolysis ofcigarette paper produced in accordance with Examples 4 to 7,representative of the practice of this invention.

Further modification, additionally to improve the taste and aroma ofcigarette paper and smoking products formed thereof, can be achieved bysubsequent treatments of the oxycellulose produced in accordance withthe practice ofthis invention, as by subjecting the cellulosic materialselectively 0x idized with nitrogen dioxide to a reduction reaction witha borohydride or nascent hydrogen, as described in our copendingapplication filed concurrently herewith and titled Method forPreparation of Smoking Products with Selective Reduction FollowingSelective Oxidation."

For this purpose, the cellulosic fibers, which have previously beenoxidized with nitrogen dioxide (gaseous or liquid) are reacted in adilute aqueous solution of a borohydride under conditions which operateto effect a reduction reaction. As the borohydride, use can be made ofalkali metal and ammonium borohydride or alkaline earth metalborohydrides, but it is preferred to make use of an alkali metalborohydride such as the borohydride of sodium, potassium or lithium.Beneficial results are secured with solutions containing the borohydridedissolved in aqueous medium in an amount within the range of 0.5 to 5percent by weight and preferably within the range of 0.1 to 1 percent byweight. With such solutions, it is desirable to carry out the reactionwith materials present in the ratio of one part by weight of theoxidized ccllu losic derivative to l0 to 1,000 parts by weight of thesolution and preferably 20 to parts by weight of the solution. The timeof exposure for reaction is not critical since beneficial results can besecured with a residence time of l minute or more but it is preferred tomake use of a reaction time within the range of5 to 60 minutes.

Solution of the borohydride in aqueous medium usually results in analkaline solution having a pH above 7. When use is made ofa borohydridesolution having an alkaline pH, there is a tendency for the oxidizedcellulosic material to be taken into solution.

We have found that the desired reduction reaction with a minimum ofdegradation or dissolution can be achieved by adjustment of the solutionof the borohydride to a pH of 7 or below but not below 3 and preferablywithin the range of 6 to 7. At a pH below 3, the borohydride becomes toounstable. The pH adjustment to the desired level can be achieved with anorganic acid, such as oxalic acid, acetic acid or glucuronic acid,oxidized cellulose or the like water soluble organic acid or by the useof an inorganic acid such as hydrochloric acid and the like. It ispreferred to make use of an organic acid such as oxalic acid, otherwisesubsequent treatment would be required for removal of undesirable ions,such as the chloride ions and the like materials introduced by the acid.In the preferred use of oxalic acid, any of the latter which remains asa residue need not be removed since beneficial use can be made of oxalicacid to produce oxalates for mineralizing the smoking product and toneutralize heavy metal ions which might otherwise be present.

Under the conditions described, the reaction can be carried out at atemperature within the range of 0 to 30 C. and preferably within therange of 0to 25 C.

This concept will now be illustrated by way of example.

EXAMPLE 8 Cellulosic paper fibers previously oxidized, as in Examples 4to 7, are immersed in a 0.2 percent water solution of sodium borohydridein which the pH has been adjusted with oxalic acid to within the rangeof 6.5 to 7. Exposure in the ratio of about one part by weightoxycellulose to 100 parts by weight of solution is continued for from Ito minutes. Thereafter, the solution is drained from the oxidizedcellulosic material and the treated fibers are rinsed with one or moreincrements of deionized water.

Others of the alkali metal and ammonimum hydrides or borohydrides can besubstituted, in whole or in part, for the sodium borohydride of Example8 in solution in concentrations within the range of 0.1 to 1 percent byweight.

Instead of borohydride reduction, a beneficial reduction reaction can beachieved by the use of hydrogen freshly released from the negative poleof an electrolytic cell in which the oxidized cellulosic material isimmersed, as illustrated by the following example. This example findsbeat use in the treatment in a continuous operation of an endless web ofcigarette paper previously oxidized as in the manner of Example 4.

EXAMPLE 9 The oxidized cellulosic cigarette paper is passed betweenhorizontally disposed, vertically spaced-apart poles of an electrolyticcell with the negative pole lowermost in the form ofa metal gauze ormetal screen. A plastic screen such as porous polyethylene is'positionedto separate the oxidized cellulosic paper from the positive pole. Use ismade of an electrolyte formulated of oxalic acid dissolved in aqueousmedium in an amount within the range of 0.1 to 40 percent by weight anda current having a density of 5 to 50 a./cm. of screen area is passedbetween the poles while the electrolyte is maintained at ambienttemperature.

Hydrogen gas bubbles up from the negative pole through the web ofoxidized cellulosic material as it is advanced continuously through thecell. The freshly formed nascent hydrogen is effective to reduce atleast some of the nitro, quinone, keto or aldehyde groups andunsaturates in the oxidized cellulosic paper fibers. Upon issuance fromthe electrolyte, the treated web is rinsed with one or more incrementsof water and dried.

The reduction treatment described is not essential to the preparation ofan improved cigarette or cigar wrapper but it will be found that suchreduction still further improves the taste and aroma upon pyrolysis ofthe paper, whereby an improved smoking product can be secured. 7

By way of a still further modification, instead of introducing themineralizing or ashing ingredients prior to oxidation, some advantagecan be derived from the introduction of the ashing components afteroxidation has been carried out whereby, with or without reduction,calcium and/or magnesium oxalate or the like ashing ingredients can beembodied as an internal component formed in situ within the cellulosicsystem, although limited benefits are derived when the ashingingredients are applied externally onto the oxidized cellulosic fibers.it appears, at present, that the use of calcium or mag nesium oxalate ispreferably since such oxalates, when incorporated within the fibers ofthe oxidized cellulosic material, are effective ash-producing agents.Moreover, the oxalates do not have the side effects of producingundesirable odors or of affecting the combustion rate of the material.It is believed that the oxalate anion is sufficiently refractory tomaintain the calcium or magnesium as an oxalate while the oxidizedcellulose is undergoing pyrolysis. This prevents the immediate formationof calcium or magnesium polyuronate and the corresponding pyrolytic odoreffects, reminiscent of ketones as produced by the pyrolysis of organiccalcium salts.

The aforesaid oxalates are insoluble and therefore the problem is toprovide means whereby such normally insoluble ash-forming materials maybe incorporated into the fibers of the oxidized cellulose. We havediscovered a number of ways in which such mineralizing materials can beintroduced into the fibers of the oxidized cellulosic material.

For example, if oxidized cellulose is the starting product,incorporation of the oxalate into the fibers can be achieved by firstsoaking the oxidized cellulose in a soluble mineral salt solution suchas a dilute solution of calcium acetate. The cation readily incorporatesitself into the oxidized cellulosic material to form the calcium salt ofthe oxidized cellulose which can be described as a calcium polyuronate.This treatment is followed by a soaking in a solution of oxalic acidwhereby the calcium polyuronate reacts with the oxalic acid whichregenerates the polyuronic acid and produces insoluble calcium oxalateas an internal component inside the oxidized cellulosic fibers. Aceticacid which is formed during the replacement reaction and any excessoxalic acid is removed from the treated cellulosic material by means ofawater wash.

The calcium can be introduced in the dissolved state in an aqueousmedium in which the oxidized cellulosic material is suspended andwherein the calcium ion is made available for reaction to form insolublecalcium polyuronate. For this purpose, the calcium may be introduced asa water soluble salt such as calcium acetate, calcium chloride, calciumglucu ronate, calcium bicarbonate, or the like, but it is preferred tomake the calcium available for reaction with the oxidized cellulosicmaterial by means of dissolving chalk or lime (slaked lime or preferablyquicklime) in an acidic aqueous medium into which the oxidizedcellulosic material is introduced to take up calcium to form insolublecalcium polyuronate. Thereafter oxalic acid is added whereby the oxalicacid which diffuses into the fiber is taken up by the calcium to formthe calcium oxalate in situ within the cellulosic fiber, and thus toregenerate the oxidized cellulosic material in its original acidiccondition.

When use is made of lime as the source of calcium, the acidic aqueousmedium to which the calcium is added can be formulated from an organicor inorganic acid, such as acetic acid, nitric acid, hydrochloric acid,glucuronic acid and the like, with the acid present in an amount toprovide an acidic solution having a pH less than 7 and preferably a pHwithin the range of4 to 5. With hydrochloric acid or with acetic acid,the desired level can be obtained with the acid present in the aqueousmedium in an amount within the range of 0.1 to 2 percent by weight. ThepH of the solution into which the oxidized cellulose is introducedshould not exceed 6.5, otherwise the oxidized cellulosic material willtend to dissolve therein. As a result, lime should not be added in anamount which will operate to raise the pH above 6.5 and it is preferredto add lime in an amount to raise the pH of the acidic aqueous medium towithin the range of 4 to 6, and preferably about 5. For this purpose,lime can be added in an amount within the range of 0.01 to 4 percent byweight and preferably in an amount within the range of 0.01 to 1 percentby weight and still more preferably in an amount within the range of0.02 to 0.05 percent by weight. Calcium oxide readily dissolves in theacidic aqueous medium to form the corresponding calcium salt. Theaddition of lime will operate to raise the pH of the solution. To avoidlocalized effects, it is preferred to conduct the calcium replenishmentin a portion of the liquid separate from the por- .tion containing theoxidized cellulose.

The oxidized cellulosic material, after taking up a suitable quantity ofcalcium ion, is then reacted with at least a stoichiometric amount ofoxalic acid in solution in aqueous medium at a pH within the range of 2to 7 and preferably within the range of 3 to 5. Calcium is taken fromthe calcium polyuronate to form the corresponding calcium oxalate insitu in the oxidized cellulosic fibers. Calcium oxalate is comparativelystable by comparison with the oxidized cellulosic material so that itwill remain while the cellulosic material is being pyrolyzed duringsmoking of the smoking product.

The reaction to form the calcium oxalate is not critically dependentupon temperature. However, it is preferred to carry out the describedreaction at a temperature within the range of to 40 C. with a reactiontime of to l0 minutes. Longer times can be used but will be unnecessary.

Instead, the mineralizing agents can be introduced into the oxidizedcellulosic material in the manner previously described by introductioninto the paper or cellulosic fiber and as illustrated in Examples 1 to3, but with the oxidized cellulosic material substituted for thecellulosic paper or pulp.

The foregoing concepts of mineralizing the cellulosic material afteroxidation reaction are illustrated by the following examples.

EXAMPLE l0 Oxidized cellulose, prepared in accordance with Examples 4 to7, or oxidized cellulose which has been reduced in accordance withExamples 9 and is introduced into a reaction vessel with sufficientwater to provide mobility of the slurry upon stirring. Acetic acid isadded to provide a concentration of 2 percent by weight and the lime isadded in an amount to provide an ash level of about 5 percent whencompletely absorbed by the oxidized cellulosic material. The pH of thesolution will rise from 4 to about 5 and as the calcium cation is takenup by the oxidized cellulose, the pH of the solution will fall back toabout 4. After about 5 minutes at ambient temperature, oxalic acid isadded in a stoichiometric amount with a drop in pH to about 3. As theoxalic acid is absorbed into the fibers by reaction with calcium to formcalcium oxalate, the pH ofthe system will rise again to about 4.

The foregoing cycle may be repeated a number of times to produce anoxidized cellulosic material containing calcium oxalate internallydispersed with the fibrous system in an amount corresponding to 5 to 45percent by weight calculated on calcium carbonate ash level.

After the final cycle, the treated oxidized cellulosic material isthoroughly washed with deionized water to remove excess oxalic acid andthe resulting cellulosic material is dried.

The cellulosic pulp which has been oxidized and ashed can be suspendedin aqueous medium to form a funish used in the preparation of paper.

EXAMPLE ll The process of Example 10 is repeated except that the paperthat is formed and dried is subsequently wet with an aqueous solutioncontaining 0.25 percent by weight oxalic acid to reintroduce oxalic acidinto the formed paper.

EXAMPLE 12 The process of Example 10 is repeated but instead of treatingthe oxidized cellulosic material with lime dissolved in acetic acid, theoxidized cellulosic material is treated directly with an aqueoussolution containing about 0.1 percent by weight calcium acetate followedby the introduction of the solution of oxalic acid.

EXAMPLE 13 The procedure of Examples 10, l l, and 12 is followed exceptthat magnesium, strontium or barium oxide or acetate are substituted inequivalent amounts for the calcium oxide and instead of making use ofoxalic acid, tannic acid is substituted to form the correspondingtannate.

EXAMPLE 14 A 5 percent solution of calcium acetate is provided in onecontainer and a 6 percent solution of oxalic acid is provided in anotherand the two solutions are mixed one with the other and immediatelyapplied by spraying onto the oxidized cellulosic material. Applicationis made while the materials are maintained at a temperature within therange of 0 to 10 C. to provide the oxidized cellulosic material withcalcium oxalate which remains soluble for a period of time to enablepenetration into the oxidized cellulosic system and which thereafterprecipitates out upon loss of water of hydration. After aging thematerial for 10 to 30 minutes to allow precipitation to be completed,the oxidized cellulosic material is washed with water to remove solublesalts and the resulting product is dried. The application can be made anumber of times to provide the desired ash level. The foregoingapplications may be made with the oxidized cellulose in the form of pulpor in the form of paper to incorporated the desired ashing ingredients.When in the final form, the dried paper of ashed and oxidized cellulosicmaterial may be treated with a O.l to 0.5 percent by weight solution ofoxalic acid in deionized water to incorporate up to 5 percent by weightof oxalic acid into the fibrous system.

The cellulosic materials and paper formed thereof in accordance with theforegoing description may be further processed in the manners describedin the aforementioned copending applications to incorporate variousagents such as agents for controlling the burning rate by the additionof potassium, rubidium or cesium salts, or the addition of agents toprovide neutralization of the smoke, such as by the addition of ammonia,or amine salts or nicotine, or by the introduction of agents forgeneration ofincreased amounts of smoke as by the introduction of fattyacids, esters and ethers, and the introduction of coloring agents, allas described in the aforementioned copending parent application.

It will be apparent from the foregoing that we have provided a cigarettepaper and method and means for producing same wherein the taste andaroma of the cigarette paper during pyrolization and during the burningof the smoking product wrapped therein are markedly improved. Suchpapers or wrappers, produced in accordance with the practice ofthisinvention, find beneficial use with current smoking products or smokingproducts of the type fabricated ofcellulosic materials or othersynthesized smoking products.

it will be understood that changes may be made in the details offormulation and operation without departing from the spirit of theinvention, especially as defined in the following claims.

We claim:

1. In the method of producing a cellulosic wrapper for smokable materialin the fabrication of cigarettes and cigars, the steps of providing apaper of cellulosic fiber for wrapping smokable material in thefabrication of cigarettes and cigars, uniformly distributing throughoutthe cellulosic fibers of the paper 5 to 45 percent by weight of anashing ingredient in the form ofa salt having a cation in the form of analkaline earth metal and an anion selected from the group consisting ofoxalic acid, tannic acid, pivalic acid, glycolic acid, diglycolic acidand lactic acid, sheeting the paper before or after treatment to wrapperform, and packaging the smokable material within the treated wrapper toproduce the cigarette or cigar.

2. The method as claimed in claim 1 in which the cation is selected fromthe group consisting of calcium, magnesium, strontium, and barium.

3. The method as claimed in claim 1 in which the ashing ingredientcomprises a mixture of calcium oxalate and magnesium oxalate present inthe ratio of one part by weight magnesium oxalate to one to four partsby weight calcium oxalate.

4. The method as claimed in claim 1 in which the ashing ingredient isintroduced by the steps of wetting the cellulosic material with the saltwhile in a solubilized state in aqueous medium and aging the treatedfibers to precipitate the salt in situ within the cellulosic fibrousstructure.

5. The method as claimed in claim 4 comprising the steps of providingone aqueous solution containing the cation and a second aqueous solutioncontaining the anion and substantially simultaneously wettin thecellulosic material with the solutions.

6. The method as claimed in claim 5 in which the solutions are admixedimmediately prior to wetting the cellulosic material.

7. The method as claimed in claim 5 in which the solutions areseparately applied substantially simultaneously onto the cellulosicmaterial.

8. The method as claimed in claim 1 in which the ashing ingredient isintroduced into the cellulosic fibers prior to paper formation and whichincludes the step of forming the cellulosic fibers into a thin paperwrapper and rinsing the formed paper with waterto remove water solublesand then drying the paper.

9. The method as claimed in claim 8 which includes the step ofintroducing an acid into the treated paper in an amount up to 0.5percent by weight of the paper in which the acid is selected from thegroup consisting of oxalic acid, tannic acid, pivalic acid, glycolicacid, diglycolic acid, and lactic acid.

10. The method as claimed in claim 8 in which the acid is oxalic acid.

11. The method as claimed in claim 1 in which the salt is present in anamount of at least percent by weight of the cellulosic fibers and theremainder making up the ashing component is a filler selected from thegroup consisting of perlite, talc, alumina, silica, and calciumcarbonate.

12. The method as claimed in claim 1 which includes the additional stepof oxidizing the cellulosic material with nitrogen dioxide selectivelyto oxidize methylol groups on the C, position of the cellulosic moleculeby an amount within the range of to 60 Percent.

13. The method as claimed in claim 12 in which the nitrogen dioxideoxidizing medium is liquid nitrogen dioxide and which includes the stepof separating the liquid oxidizing medium from the oxidized cellulosicfiber upon completion of the oxidation reaction.

14. The method as claimed in claim 12 in which the cellulosic materialis oxidized by an amount insufficient to destroy the fibrouscharacteristics of the cellulosic material.

15. The method as claimed in claim 12 in which the cellulosic materialis oxidized by an amount within the range of 40 to 60 percent.

16. The method as claimed in claim 13 which includes the step ofbubbling an oxygen containing gas through the liquid nitrogen dioxideduring the oxidation reaction.

17. The method as claimed in claim 12 in which the liquid oxidizingmedium contains up to 8 percent by weight water.

18. The method as claimed in claim 17 in which the amount of water iswithin the range of 0.5 to 5 percent in the oxidizing medium.

19. The method as claimed in claim 13 in which the oxidation is carriedout at a temperature within the range of 15 to 65 C.

20. The method as claimed in claim 13 which includes the step of rinsingthe oxidized fibers with anhydrous liquid nitrogen dioxide afterseparating the liquid oxidizing medium from the oxidized cellulosefibers.

21. The method as claimed in claim 12 which includes the step ofsubjecting the oxidized cellulosic material to a mild reductionreaction.

22. The method as claimed in claim 21 in which the reduction reaction iscarried out with a reducing agent selected from the group consisting offreshly prepared hydrogen and a borohydrate.

23. The method as claimed in claim 12 which includes the step of addingan acid to the dried oxidized cellulosic material in an amount up to 5percent by weight and in which the acid is selected from the groupconsisting of oxalic acid, tannic acid, pivalic acid, glycolic acid,diglycolic acid, and lactic acid.

24. The method as claimed in claim 23 in which the applied acid isoxalic acid.

2. The method as claimed in claim 1 in which the cation is selected fromthe group consisting of calcium, magnesium, strontium, and barium. 3.The method as claimed in claim 1 in which the ashing ingredientcomprises a mixture of calcium oxalate and magnesium oxalate present inthe ratio of one part by weight magnesium oxalate to one to four partsby weight calcium oxalate.
 4. The method as claimed in claim 1 in whichthe ashing ingredient is introduced by the steps of wetting thecellulosic material with the salt while in a solubilized state inaqueous medium and aging the treated fibers to precipitate the salt insitu within the cellulosic fibrous structure.
 5. The method as claimedin claim 4 comprising the steps of providing one aqueous solutioncontaining the cation and a second aqueous solution containing the anionand substantially simultaneously wetting the cellulosic material withthe solutions.
 6. The method as claimed in claim 5 in which thesolutions are admixed immediately prior to wetting the cellulosicmaterial.
 7. The method as claimed in claim 5 in which the solutions areseparately applied substantially simultaneously onto the cellulosicmaterial.
 8. The method as claimed in claim 1 in which the ashingingredient is introduced into the cellulosic fibers prior to paperformation and which includes the step of forming the ceLlulosic fibersinto a thin paper wrapper and rinsing the formed paper with water toremove water solubles and then drying the paper.
 9. The method asclaimed in claim 8 which includes the step of introducing an acid intothe treated paper in an amount up to 0.5 percent by weight of the paperin which the acid is selected from the group consisting of oxalic acid,tannic acid, pivalic acid, glycolic acid, diglycolic acid, and lacticacid.
 10. The method as claimed in claim 8 in which the acid is oxalicacid.
 11. The method as claimed in claim 1 in which the salt is presentin an amount of at least 5 percent by weight of the cellulosic fibersand the remainder making up the ashing component is a filler selectedfrom the group consisting of perlite, talc, alumina, silica, and calciumcarbonate.
 12. The method as claimed in claim 1 which includes theadditional step of oxidizing the cellulosic material with nitrogendioxide selectively to oxidize methylol groups on the C6 position of thecellulosic molecule by an amount within the range of 15 to 60 percent.13. The method as claimed in claim 12 in which the nitrogen dioxideoxidizing medium is liquid nitrogen dioxide and which includes the stepof separating the liquid oxidizing medium from the oxidized cellulosicfiber upon completion of the oxidation reaction.
 14. The method asclaimed in claim 12 in which the cellulosic material is oxidized by anamount insufficient to destroy the fibrous characteristics of thecellulosic material.
 15. The method as claimed in claim 12 in which thecellulosic material is oxidized by an amount within the range of 40 to60 percent.
 16. The method as claimed in claim 13 which includes thestep of bubbling an oxygen containing gas through the liquid nitrogendioxide during the oxidation reaction.
 17. The method as claimed inclaim 12 in which the liquid oxidizing medium contains up to 8 percentby weight water.
 18. The method as claimed in claim 17 in which theamount of water is within the range of 0.5 to 5 percent in the oxidizingmedium.
 19. The method as claimed in claim 13 in which the oxidation iscarried out at a temperature within the range of 15* to 65* C.
 20. Themethod as claimed in claim 13 which includes the step of rinsing theoxidized fibers with anhydrous liquid nitrogen dioxide after separatingthe liquid oxidizing medium from the oxidized cellulose fibers.
 21. Themethod as claimed in claim 12 which includes the step of subjecting theoxidized cellulosic material to a mild reduction reaction.
 22. Themethod as claimed in claim 21 in which the reduction reaction is carriedout with a reducing agent selected from the group consisting of freshlyprepared hydrogen and a borohydrate.
 23. The method as claimed in claim12 which includes the step of adding an acid to the dried oxidizedcellulosic material in an amount up to 5 percent by weight and in whichthe acid is selected from the group consisting of oxalic acid, tannicacid, pivalic acid, glycolic acid, diglycolic acid, and lactic acid. 24.The method as claimed in claim 23 in which the applied acid is oxalicacid.